Ocular Dominance Plasticity: The Visual Cortex Critical Period

Monocular Deprivation

Cortical Maturation

Age (critical-period clock) 0

Digest PNNs (ChABC) — reopen plasticity

Live Readouts

Right dominantODI = 0.00Left dominant

Plasticity rate η

100%

Columns polarized

PNN density (molecular brake)

How it works

Each of the 484 cortical columns holds two competing synaptic weights, w_L and w_R, for input driven by the left and right eye. They compete for a fixed synaptic resource (w_L+w_R=1) under a normalized Hebbian ("fire together, wire together") rule:

r        = wL·aL + wR·aR            (postsynaptic response)
dwL/dt   = η·(aL·r − k·wL)          (Oja-style Hebbian term)
dwR/dt   = η·(aR·r − k·wR)
then renormalize wL+wR = 1          (competition for fixed resource)

a_L, a_R are the two eyes' driving activity — equal and noisy when both eyes are open, collapsed to a fifth of normal for the deprived eye during monocular deprivation. Ocular dominance index ODI = w_L − w_R tracks which eye owns each column.

The learning rate itself is gated by a molecular brake — perineuronal nets (PNNs) that mature with age and physically restrict synaptic rearrangement:

η(age) = η_max / (1 + 6·PNN²),   PNN = age / 100

This is why monocular deprivation causes permanent amblyopia in a young visual cortex (Hubel & Wiesel's classic experiments) but barely shifts an adult one — and why enzymatically digesting PNNs with chondroitinase ABC (ChABC) can experimentally reopen plasticity at any age, which this simulator models by forcing PNN → 0.

Left-eye dominant column Balanced (binocular) Right-eye dominant column

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